A reed valve typically includes a cage which is located in a flow passage so that the cage spans the cross section of the passage. The cage has several cage ports allowing fluid flow therethrough. A petal consisting of a flat, flexible member is pivotably connected to the downstream side of the cage adjacent each cage port so that the petal covers the cage port. A stop, which may comprise a plate, can be attached to the cage to limit the deflection of the petal away from the cage.
Fluid having sufficiently high pressure upstream of the cage causes the petal to begin to deflect away from the cage allowing fluid flow through the cage port thereby opening the reed valve. After the petal deflection is initiated, the petal oscillates between the cage and the stop. The duration of the opening of the reed valve (i.e., the petal being deflected away from the cage) is believed to be dependent on the petal structure and engine operating conditions.
When the pressure of the fluid upstream of the cage becomes less than the pressure downstream of the cage, the petal will return to the cage thereby obstructing the cage port and closing the reed valve. In this position, the petal obstructs fluid back-flow from downstream of the cage through the cage port.
When a reed valve is located in an intake passage leading to a cylinder of an engine, a trapped volume is defined by the portion of the intake passage between the reed valve and an intake valve seated in the intake passage between the reed valve and cylinder. Such an arrangement can be used in conjunction with an intake valve which remains open after the intake phase of the engine cycle and during the initial part of the compression phase of the engine cycle. Opening of the intake valve during the compression phase allows additional fluid to flow into the cylinder at some engine operating conditions, but can also result in fluid flowing out of the cylinder back into the trapped volume at other engine operating conditions. The reed valve obstructs such fluid back-flow further into the intake passage resulting in improved engine performance as compared to an engine employing the same intake valve timing without a reed valve.
The improvements in engine performance resulting from the use of a reed valve with such an intake valve can be limited if certain reed petal structures are used and the engine is operated at certain speeds. These limitations in engine performance are believed to be due, in part, to the petal structure. A specific petal structure can result in acceptable durations of petal deflection for most engine operating speeds, yet remain deflected away from the cage during some engine operating speeds after the fluid flow toward the cylinder has ceased and the fluid back-flow out of the cylinder has begun. Such a condition can result in a significant reduction in the ability of the reed valve to obstruct fluid back-flow. Since the petal structure is fixed in a typical reed valve, it can be difficult to select a petal structure which does not remain deflected away from the cage after the intake phase, during at least some of the broad range of engine operating speeds.
A delay in the opening of the reed valve with respect to the beginning of the intake phase can occur during some engine operating speeds and is believed to also contribute to deflection of the petal after the fluid flow toward the cylinder has ceased during such engine operating speeds. This is due to the petal deflection duration being primarily dependent upon the petal structure and engine operating speed. Thus, a delay in the opening of the reed valve can cause a consequent delay in the closing of the reed valve.
A delay in the opening of the reed valve can be caused by the trapped volume having a pressure substantially higher than the pressure upstream of the reed valve. Such an elevated pressure in the trapped volume can be caused by the intake valve remaining open during the initial part of the compression phase in the cylinder. Such an elevated pressure in the trapped volume must be reduced so that it is less than the pressure upstream of the petal in order for the petal to begin to deflect away from the cage. Ordinarily, the increased pressure in the trapped volume is maintained until the intake phase begins when the increased pressure is vented to the cylinder. The time required for the pressure reduction can cause the delay in the reed valve opening.